1. Field of the Invention
This invention relates to an image reading device and, more particularly, to an image reading device in which a read image is directly output to a monitor receiver, video printer, video tape recorder (VTR) or the like.
2. Description of the Prior Art
In the conventional image reading device, an original is scanned and read, using a line sensor, that is a one-dimensional or linear array of charge coupled devices or CCDs, and the read image signals are converted by an analog to digital (A/D) converter into digital video signals, which are then input via digital interface, such as GPLB, RS232C or SCSI, into a large capacity memory in computer for storage. When the stored image data are to be displayed on a monitor receiver or printed by a video printer, various signal processing operations are performed on the video data by a computer before the display or printing data are transmitted to the monitor receiver or video printer.
Therefore, when the video data read by the video reading device are simply displayed on the monitor receiver or printed on the video printer, a computer or the like processing device is necessitated. On the other hand, video data read from the video reading device are transmitted to the processing device, such as the computer, by a time-consuming operation, while it taken much time since the original is read until the read original is displayed on the monitor receiver.
In the conventional image reading device, if the enlargement ratio when the picture original of the JIS (Japanese Industrial Standard) size A-4 format is read and displayed on the full size screen of a display device, such as CRT monitor, is set to a standard enlargement ratio equal to 1, an A-5 or A-6 format region in the original, for example, may be displayed on the full-size screen of the display screen by changing this enlargement ratio.
It is now assumed that, as shown in FIG. 1, a picture original GD of a predetermined format is placed on an original table DS of the image reading device so that the lower left end of the original GD coincides with the origine 0 of the original table DS, the original GD is read by relative movement of the line sensor LS in the sub-scanning direction X with respect to the original GD, and the thus read video data are displayed on a display apparatus, such as CRT monitor. In such case, if the enlargement ratio of the image reading device is switched to, for example, 1, 2 and 4, indications are made on the display device, an shown on the display screen SC at (a), (b) and (c) in FIG. 2, respectively.
With the size of the picture original GD of FIG. 2 of, for example, A-4 format, the region of the overall A-4 format of the picture original GD is read when the enlargement ratio is "1", so that display is made on the overall surface of the display screen SC of FIG. 2(a). With the enlargement ratio of "2", a region R.sub.A5 (A-5 format) of a similar figure portion with one half area of the area of the original GD with the origin 0 as the lower left end is read and displayed on the overall surface of the display screen SC of FIG. 2(b). With the enlargement ratio of "4", a region R.sub.A6 (A-6 format) of a similar figure portion with one-fourth the area of the original GD with the origin 0 as the lower left end is read and displayed on the overall surface of the display screen SC of FIG. 2(c).
With the above described conventional image reading device, plural regions having sizes consistent with plural enlargement ratio are preset as the image reading range with the origin 0 of the original table DS as the lower left end. Since the original is read with the original placed in the reversed position on the original table, it is not grasped, until reaching the end of reading, what range of the original is being read. Also, since the image reading range on the original table is determined in dependence upon the selected enlargement ratio, it is not possible with the conventional device to read an arbitrarily selected portion of the picture original to display it after enlargement to a full screen size.
Although it is contemplated to designate the image reading range after shifting from the origin 0, the image reading range is determined by designating the reading start position from the origin 0 by units of millimeters, thus by the user's intuitive sense. It is also not apparent if the described portion of the original is being read until the original is actually read and the image displayed.
In the field of duplicators, there is known a technique of automatically setting the contracting or enlarging ratio of the duplicator (Japanese Patent Publication SHO-57-68868(1982)). This device is adapted to automatically set the contracting and enlarging ratio of the original documents of different sizes, but is not an image reading device in which the read image is directly displayed on the display device, while it is not adapted to read only a portion of the read image for display with an enlarged scale.